/*
 * Copyright  2000-2004 The Apache Software Foundation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); 
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License. 
 *
 */
package org.apache.bcel.generic;

import java.io.DataOutputStream;
import java.io.IOException;

import org.apache.bcel.Constants;
import org.apache.bcel.util.ByteSequence;

/**
 * Abstract super class for instructions dealing with local variables.
 *
 * @version $Id: LocalVariableInstruction.java,v 1.1 2007/06/04 00:00:46 liqiang2000 Exp $
 * @author  <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
 */
public abstract class LocalVariableInstruction extends Instruction implements TypedInstruction,
        IndexedInstruction {

    protected int n = -1; // index of referenced variable
    private short c_tag = -1; // compact version, such as ILOAD_0
    private short canon_tag = -1; // canonical tag such as ILOAD


    private final boolean wide() {
        return n > Constants.MAX_BYTE;
    }


    /**
     * Empty constructor needed for the Class.newInstance() statement in
     * Instruction.readInstruction(). Not to be used otherwise.
     * tag and length are defined in readInstruction and initFromFile, respectively.
     */
    LocalVariableInstruction(short canon_tag, short c_tag) {
        super();
        this.canon_tag = canon_tag;
        this.c_tag = c_tag;
    }


    /**
     * Empty constructor needed for the Class.newInstance() statement in
     * Instruction.readInstruction(). Also used by IINC()!
     */
    LocalVariableInstruction() {
    }


    /**
     * @param opcode Instruction opcode
     * @param c_tag Instruction number for compact version, ALOAD_0, e.g.
     * @param n local variable index (unsigned short)
     */
    protected LocalVariableInstruction(short opcode, short c_tag, int n) {
        super(opcode, (short) 2);
        this.c_tag = c_tag;
        canon_tag = opcode;
        setIndex(n);
    }


    /**
     * Dump instruction as byte code to stream out.
     * @param out Output stream
     */
    public void dump( DataOutputStream out ) throws IOException {
        if (wide()) {
            out.writeByte(Constants.WIDE);
        }
        out.writeByte(opcode);
        if (length > 1) { // Otherwise ILOAD_n, instruction, e.g.
            if (wide()) {
                out.writeShort(n);
            } else {
                out.writeByte(n);
            }
        }
    }


    /**
     * Long output format:
     *
     * &lt;name of opcode&gt; "["&lt;opcode number&gt;"]" 
     * "("&lt;length of instruction&gt;")" "&lt;"&lt; local variable index&gt;"&gt;"
     *
     * @param verbose long/short format switch
     * @return mnemonic for instruction
     */
    public String toString( boolean verbose ) {
        if (((opcode >= Constants.ILOAD_0) && (opcode <= Constants.ALOAD_3))
                || ((opcode >= Constants.ISTORE_0) && (opcode <= Constants.ASTORE_3))) {
            return super.toString(verbose);
        } else {
            return super.toString(verbose) + " " + n;
        }
    }


    /**
     * Read needed data (e.g. index) from file.
     * PRE: (ILOAD <= tag <= ALOAD_3) || (ISTORE <= tag <= ASTORE_3)
     */
    protected void initFromFile( ByteSequence bytes, boolean wide ) throws IOException {
        if (wide) {
            n = bytes.readUnsignedShort();
            length = 4;
        } else if (((opcode >= Constants.ILOAD) && (opcode <= Constants.ALOAD))
                || ((opcode >= Constants.ISTORE) && (opcode <= Constants.ASTORE))) {
            n = bytes.readUnsignedByte();
            length = 2;
        } else if (opcode <= Constants.ALOAD_3) { // compact load instruction such as ILOAD_2
            n = (opcode - Constants.ILOAD_0) % 4;
            length = 1;
        } else { // Assert ISTORE_0 <= tag <= ASTORE_3
            n = (opcode - Constants.ISTORE_0) % 4;
            length = 1;
        }
    }


    /**
     * @return local variable index  referred by this instruction.
     */
    public final int getIndex() {
        return n;
    }


    /**
     * Set the local variable index
     */
    public void setIndex( int n ) {
        if ((n < 0) || (n > Constants.MAX_SHORT)) {
            throw new ClassGenException("Illegal value: " + n);
        }
        this.n = n;
        if (n >= 0 && n <= 3) { // Use more compact instruction xLOAD_n
            opcode = (short) (c_tag + n);
            length = 1;
        } else {
            opcode = canon_tag;
            if (wide()) {
                length = 4;
            } else {
                length = 2;
            }
        }
    }


    /** @return canonical tag for instruction, e.g., ALOAD for ALOAD_0
     */
    public short getCanonicalTag() {
        return canon_tag;
    }


    /**
     * Returns the type associated with the instruction - 
     * in case of ALOAD or ASTORE Type.OBJECT is returned.
     * This is just a bit incorrect, because ALOAD and ASTORE
     * may work on every ReferenceType (including Type.NULL) and
     * ASTORE may even work on a ReturnaddressType .
     * @return type associated with the instruction
     */
    public Type getType( ConstantPoolGen cp ) {
        switch (canon_tag) {
            case Constants.ILOAD:
            case Constants.ISTORE:
                return Type.INT;
            case Constants.LLOAD:
            case Constants.LSTORE:
                return Type.LONG;
            case Constants.DLOAD:
            case Constants.DSTORE:
                return Type.DOUBLE;
            case Constants.FLOAD:
            case Constants.FSTORE:
                return Type.FLOAT;
            case Constants.ALOAD:
            case Constants.ASTORE:
                return Type.OBJECT;
            default:
                throw new ClassGenException("Oops: unknown case in switch" + canon_tag);
        }
    }
}
